Integrated circuits are solid state devices in which electrical components and electrical connections between the components are incorporated into a solid matrix. The electrical components and connections are produced by the strategic placement of various conducting, semiconducting and insulating materials to form and encapsulate the desired circuit in the composite solid matrix. The development of the integrated circuit has led to the miniaturization of electronics by providing a strong matrix to support and protect fragile miniaturized components and connections and by facilitating the placement of the electrical components in close proximity. The integrated circuit has further served to increase the reliability of electronic devices by the elimination of moving parts and fragile electrical wiring and connections.
Integrated circuits are typically mass produced by forming hundreds of circuits, called dice, on a semiconductor substrate, or "wafer". The circuits are formed by depositing a series of individual layers of predetermined materials on the wafer. The individual layers of the integrated circuit are, in turn, produced by a series of manufacturing steps. The precise characteristics of the layers, such as composition, thickness, and surface quality, uniquely determine the electronic properties and the performance of the integrated circuit.
The integrated circuits must be produced in a clean environment to prevent contamination of the layers by foreign matter that will degrade the performance of circuits. Contamination level requirements in semiconductor wafer processing areas ("clean rooms") are typically less than 1 particle/ft.sup.3 air (referred to as Class 1 cleanliness). To achieve these requirements, special high volume ventilation systems are necessary to continually filter the surrounding air. The ventilation systems represent a significant contribution to the overall wafer production cost. Therefore, a significant savings can be realized by minimizing the size of the clean room, and thereby lessening the costs associated with operating the clean room.
In addition, the production of integrated circuits subjects the semiconductor wafers to a number of different processes and environmental conditions. Wafer carriers are used to store, transport, and track the wafers in bulk lots through and between the various processes. However, a single carrier is not typically suitable for exposure to all of the different environmental conditions encountered during processing. Therefore, the wafers must be transferred to more suitable carriers at various stages of processing.
Wafer transfer machines are typically used to transfer the wafers between carriers and/or boats. The machines generally include a base upon which a first carrier containing the wafers and a second empty carrier are placed in fixed opposing positions. A transfer arm is either manually or automatically translated to contact and push the wafers from the first carrier to the second carrier.
One problem with the wafer transfer machines currently used in industry is that the machines are generally capable of transferring only one size wafer or are designed for only one type of carrier or boat. As a result, a different machine must be acquired and placed in the clean room for each wafer size to be processed or each boat type used. The additional machines unnecessarily adds to the overall wafer production costs in terms of increased equipment and maintenance costs and increased clean room space requirements to house the equipment.
Another problem with current wafer transfer machines is that the surface or face of the wafers must be perpendicular to gravity to allow the wafers to be moved between carriers. Wafers are normally stored and transported in the carriers with the surface or face aligned generally parallel to the gravitational field. The additional handling of the carriers necessary to transfer the wafers in this manner increases the potential for damage to the wafers. The additional handling may also be awkward for personnel and could result in injuries.
Yet another problem with current wafer carrier machines is that wafer carriers must be constructed to allow access by the transfer arm to push the wafers between carriers. Therefore, the shape of the carrier cannot be optimized for the specific process in which the carrier is used.
In view of these and other problems, there is generally a need for improved article transfer apparatuses and methods. Specifically, there is a need for article transfer machines that can be used to perform wafer transfer operations for different size wafers and carriers with more ergonomically conducive, but less overall, handling, thereby reducing associated equipment and clean room costs and injuries to personnel.